Compensating balance wheel and the like



Aug. 4, 1942. G. SMITH 2,292,244

COMPENSATING BALANCE WHEEL AND THE LIKE Original Filed Jan. 26, 1939 Patented Aug. 4, 1942 UNITED STATES PATENT OFFICE COMPENSATING BALANCE WHEEL AND THE LIKE Graydon Smith, Cambridge, Mass., assignor to Ralph E. Thompson, Boston, Mass.

4 Claims.

This invention relates to temperature compensating devices, more particularly compensating balance wheels for clocks and the like, and the primary object of the invention resides in the production of a superior device of this nature which, due to its simple and novel construction, can be produced in mass quantities at relatively small cost. This application is a division of my copending application, Ser. No. 252,893 now Patent No. 2,232,742 dated February 25, 1941.

It is well known that the rate of movement of balance wheels used in clocks and watche varies with temperature conditions, due to the action of heat and cold more particularly on the hair spring employed. Lowering f the temperature causes the spring to become stiffer which in turn increases the rate 0f oscillation or the balance wheel, and raising of the temperature in like manner decreases the rate of the balance wheel. I am aware that compensating balance wheels have been known which automatically compensate for such changes in temperature by increasing the moment of inertia of the wheel upon lowering of the temperature, and vice versa, whereby causing the wheel to run substantially at a uniform rate at all prevailing temperatures. All of such wheels have however been expensive to produce and some have comprised a plurality of relatively loose and fragile parts. A further object of m invention resides in the production of an improved and more substantial compensating balance Wheel formed in one piece and embodying spokes of dissimilar metals having substantially different coefficients of expansion.

These and other features of the invention will be best understood and appreciated from the following description of preferred embodiments thereof selected for purposes of illustration and shown in the accompanying drawing in which,

Fig. 1 is a fragmentary view of a compound metallic strip from which one of my improved balance wheels has been blanked,

Fig. 2 is a front elevation of the blanked wheel,

Fig. 3 is an edge elevation of the wheel,

Fig. 4 is a transverse sectional view through the strip,

Fig. 5 is a fragmentary view of another compound metallic strip from which has been blanked a modified form of balance wheel,

Fig. 6 is a front elevation of the blanked wheel,

Fig. 7 is an edge elevation of the wheel.

Referring more specifically to the drawing wherein I have illustrated certain applications of my invention, In indicates a compound metallic strip comprising two relatively wide portions I2 of one metal and a relatively narrow portion 14 of another metal therebetween, the metals being dissimilar and having different coefficient of expansion. The strip is formed by rolling the combined metals to the required thickness and wherein the portion l2 and M are united at their edges into an integral unit.

In Fig. 2 is illustrated a balance wheel l5 which has been blanked from the strip Ill. The wheel comprises a hub l6, two pairs of spokes l8 and 20 and two peripheral portions 22 each supported by a pair of spokes l8 and 20. The two portions 22 are disposed at opposite sides of the hub and each comprises a relatively heavy lobe supported on and overhung from the two spokes l8 and 26.

The peripheral portions 22 of the wheel and the spokes 20 are formed from the relatively wide strip portions 12, and the spokes I 8 are formed from the narrow strip I4. The spokes 2|] are integral with the hub at their inner ends and are integral with intermediate portions of the lobes 22 at their outer ends. The spokes l8 are integral with the hub at their inner ends and have their outer ends integrally connected with the smaller ends of the members 22 at points remote from the spokes 20.

Since lowering of the temperature stiffens the hair spring cooperating with the balance wheel and thereby shortens its period of oscillation whereby speeding up the rate of the wheel, it is required that such lowering of temperature shall provide compensation by increasing the moment of inertia of the wheel. Such increase is automatically cared for by forming the spokes I8 of a metal having a greater coefficient of expansion than that of the spokes 20, whereby the lobes 22 are swung outwardly by the relatively greater contraction of the spokes l8 upon lowering of the temperature, a rise in temperature acting conversely to swing the lobes inwardly. The two metals should be such as to provide a relatively large difference in their coefiicients of expansion and I have found that Invar steel and brass provide two such metals. In the strip shown in Fig. 1 the two wide strip portions l2 may be of Invar steel and the relatively narrow strip I 4 may be of brass. The greater expansion or contraction of the brass serves in the spokes I8 to rock the lobes 22 inwardly or outwardly respectively on the spokes 20. The wheel is supported and operated on a staff 24 disposed centrally through the hub IS.

The compound strip 30 shown in Fig. 5 is like the strip 10 shown in Fig. 1 except that the relatively wide portions 32 are of a metal, such as brass, having a substantially greater coefilcient of expansion than the metal, such as Invar steel, in the narrow portion 34. The balance wheel 36 blanked from this strip comprises a bar or spoke portion 38 connected at its ends to the peripheral portions or lobes 40 at points 42, this bar 38 being blanked from the strip portion 34. The small ends of the lobes 48 overhang the spoke connections 42 at 44 and each has connected thereto one end of a spoke portion 46 extending parallel with the spoke portion 38 and having its other end integrally connected thereto at 48. The wheel is supported and operated on a staff 50 extending through the centrally disposed hub portion of the bar 38.

It will be apparent that lowering of the temperature, which causing speeding up of the rate of the balance wheel, serves through the relatively greater contraction of spoke portions 46 to throw the elements 40 outwardly, and raising of the temperature conversely serves through expansion of the portions 46 to throw the elements 40 inwardly, the elements 40 pivoting about the points 42. This construction is somewhat more sensitive than the construction illustrated in Fig. 2 since the spoke portions 46 are relatively longer (as compared with the companion spoke portions 38 and 20) than are the spoke portions I8. An important feature of the invention relates to the overhanging portion 22 or 40 of a compensating wheel or like compensating device and the cooperating relation of the spoke elements whereby a relatively small temperature change effects a considerable movement of the overhanging body due to the leverage obtained. It will also be noted that in both forms of the invention the several elements of the finished product are of uniform thickness and in a, common plane and the overhanging bodies are lobes disposed within side edges converging uniformly from the larger to the smaller ends thereof, whereby providing maximum simplicity and design and leaving no unduly projecting portions to retard free rotation of the device.

Having thus described my invention what I claim. as new and desire to secure by Letters Patent of the United States is:

1. A poly-metallic temperature compensating device, comprising a hub portion, a body portion spaced from the hub portion, and two spoke-like elements having two corresponding ends thereof integrally connected to the hub portion and the two other ends thereof integrally connected to the body portion intermediately of its ends and to one end thereof respectively, the other end of the body portion being free and relatively large and the said hub and body portions and spokelike elements being of uniform thickness and in a common plane, the two spoke-like elements being of dissimilar metals having different coeflicients of expansion.

2. A poly-metallic compensating balance wheel, comprising a hub portion, a plurality of body portions spaced from the hub portion, and two spoke-like elements connecting each body portion with the hub portion, each said two elements having two corresponding ends thereof integrally connected to the hub portion and the other two ends integrally connected to a body portion intermediately of its ends and to one end thereof respectively, the other end of the body portion being free and relatively large and the said hub and body portions and spoke-like elements being of uniform thickness and in a common plane, the two spoke-like elements being of dissimilar metals and having difierent coefficients of expansion.

3. The balance wheel defined in claim 2 in which each of said body portions comprises a lobe disposed within side edges converging unlformly from said relatively large end thereof to its other end.

4. A poly-metallic compensating balance wheel, comprising two oppositely disposed body portions. a metal strip having its ends integrally connected to the body portions intermediately of their ends, and two other metallic strips parallel with and disposed on opposite sides of the first strip and having one end of each integrally connected to the first strip and their other ends integrally connected to one end of the two body portions respectively, the other ends of the body portions being free and relatively large and the strips and body portions being of uniform thickness and in a common plane, the first strip and said two other strips being of dissimilar metals having different coeflicients of expansion.

GRAYDON SMITH. 

